Experimental study of the intrinsic permeability of municipal solid waste

Changing patterns of municipal solid waste (MSW) management, for example sorting for recycling and mechanical-biological treatment (MBT), will change the nature of the residual material going to landfill and in particular its intrinsic permeability. This is an important parameter, not least because of its influence on gas and leachate flows and the ramifications for gas and leachate management. This paper reports the results of laboratory permeability tests on specimens of MSW recovered from boreholes drilled in a Chinese landfill, under both liquid and gas flow. The test results are used to assess the intrinsic permeability of the waste, and are compared with corresponding data from raw and MBT municipal solid wastes from developed countries in the context of differences in waste composition, porosity and particle size. For the Chinese waste, the intrinsic permeability decreased with depth, while at a given depth the permeability determined with gas flow was consistently larger than that determined with liquid flow. Intrinsic permeabilities determined in liquid flow showed no clear trend of variation with effective particle diameter d₁₀, but reduced with drainable porosity (the drainable porosity, n_e, being a more appropriate and useful measure than the total porosity, n). Conversely, intrinsic permeabilities determined in gas flow showed a clear decrease with decreasing d₁₀, but no consistent variation with porosity. These differences are potentially significant in assessing the impacts and interactions between gas and liquid flows; some reasons for them are suggested.